Exhumation and preservation of Bangbule Pb-Zn-Cu deposit in West Gangdese Tectonic Belt: evidence from fission track thermochronology

The Bangbule Pb-Zn-Cu deposit is a newly discovered large-scale skarn deposit in the western part of the Gangdese Tectonic Belt in recent years. In this study, the low-temperature thermochronology method was used to reveal the cooling and exhumation history of the Bangbule deposit, evaluate the preservation of the deposit, and improve the uplift and exhumation records of the western Gangdese Tectonic Belt. Apatite fission track age in quartz porphyry is 24±2 ~ 32±3 Ma (1σ), which indicates the rapid cooling and exhumation of Bangbule deposit during the Oligocene. The simulation of thermal evolution history shows that there are three stages of cooling events in the Bangbule deposit. (Ⅰ) From the Eocene to the Late Oligocene (48~24 Ma), the cooling rate was between 4.56℃/Ma and 10.64℃/Ma and the cooling event was related to the tectonic background of India-Eurasia collision and the post-collision crustal thickening; (Ⅱ) From Late Oligocene to Middle Miocene (24~14 Ma), the cooling rate ranges from 0.38℃/Ma to 1.9℃/Ma, which is related to the tectonic background of break-off of the Indian subducted plate.(Ⅲ) From the Middle Miocene to the present (14 Ma to present), the cooling rate is between 2.28℃/Ma and 9.88℃/Ma, which is related to tectonic background of the north-south rift developed in the Gangdese Tectonic Belt.The cooling event was related to the general uplift of the Gangdese Tectonic Belt since 5 Ma ago. The exhumation thickness of the Bangbule deposit since the Eocene is between 1.5~2.5 km. The cover of the volcanic rocks of the Dianzhong Formation has played a protective role in the preservation of the deposit.